The present invention relates generally to radio communication devices. More particularly, the present invention relates to a roaming design for a Voice Over Internet Protocol handset and a related system.
Wireless Local Area Network (WLAN) systems have been developed to permit network access for portable devices. Communication is carried out using radio waves or another wireless medium. One conventional system permits radio communication between two stations in the network according to an air interface standard known as IEEE 802.11, promulgated by the Institute of Electrical and Electronics Engineers, Inc. The standard defines frequencies, modulation and data encoding for two-way communication over a radio channel. A computer such as a portable or laptop computer equipped with a suitable radio circuit can receive and transmit signals in communication with a remote radio. The remote radio may be portable as well or may be fixed.
For network access by portable devices, the network includes one or more Access Points (APs). An AP is typically fixed at a location and provides access to a wire line network. An AP serves as a base station for wireless enabled portable or fixed devices to communicate with. Such devices that communicate with an AP are referred to as client stations. The set of all stations that can communicate with each other is referred to as a basic service set (BSS). Every BSS is defined by an identification (ID) called the BSSID. The BSSID is the media access control (MAC) address in the network of the access point which serves the BSS. An extended service set (ESS) is a set of connected BSSs. APs in an ESS are connected by a distribution system. Each ESS has an ID called the SSID which is a 32-byte character string.
WLAN systems have proven to be commercially successful for providing convenient, portable network access for data devices. Users have convenient access to remotely stored data over the WLAN. When the WLAN has access to the Internet, the local user may also access all the resources of the Internet. Data communication is relatively fast and very reliable.
However, many situations require not just data communication but voice communication instead or as well. For example, a business or other enterprise may have facilities which are spread over several floors in a building or over several buildings on a campus. It is desirable for individuals to move around the building or campus and take data and voice communication with them.
At present, many users with WLAN access for data communication must use a wire line telephone for voice communication. This limits the user's mobility as the user must remain in the location of a wire line telephone. Alternatively, the user can obtain another radiotelephone device such as a cellular telephone to place and receive calls using the cellular system. However, this arrangement has several drawbacks. First, cellular coverage may be unreliable, especially inside buildings, so that a call may be dropped or unable to be completed. Further, cellular service is relatively expensive, being billed on a per-minute basis. Especially for small or medium-size companies or individuals needing voice communication services, these problems limit the value of current voice communication solutions.
Telephones using Voice Over Internet Protocol (VoIP) are known which can communicate with a WLAN. However, such devices are limited to the radio communication range of the AP. This distance may be as small as 10 meters. While this provides some user mobility, full mobility around, for example, a building or campus would be preferred.